Metallurgy - Principles and Processes - Class XII

Hardened steel on heating in the range of $220^{\circ} C$ to $330^{\circ}C$ and on slow cooling gives Hard and tough steel.

$Fe+CuSO _4\rightarrow FeSO _4+Cu$
                             Green     Reddish brown
Solution becomes green and reddish brown coating of copper is formed.

Hematite and Limonite are the most preferred ores in the extraction of iron.

Tin and zinc are commercially extracted from their respective ores by carbon reduction method.
The oxide ores of tin and zinc are reduced with carbon to form metals.

A permanent magnet is an object made from material that is magnetized and creates its own persistent magnetic field e.g. refrigerator magnet on its door. These are strongly attracted to magnets called as ferromagnetic and are made up of iron,nickel,cobalt and some alloys of rare earth metals.

Slag is a glass like by product left over after a desired metal has been separated from its ore.Slag is usually a mixture of metal oxides and silicon dioxide.These slags can contain metal sulfides and elemental metals.

Annealing is heat process whereby a metal is heated to a specific temperature/color and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily. Mild steel is heated to a red heat and allowed to cool slowly.

Iron ores have the electromagnetic property so they are concentrated by this method. An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off.

Iron is the metal of transition series which oxidizes in air to give hydrated iron oxides. Crude iron metal is produced in blast furnaces where ore is reduced by coke to pig iron which has high carbon content.

Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Iron is the best metal amongst the given options for sharp casting.

Cast iron is iron that has been shaped by being poured into a cast. It has 5% or more carbon, and the carbon separates out into flakes. This reduces the tensile strength, but not the compressive strength. Pig iron is iron as cast after smelting from ore and has a high carbon content and is an intermediate product for making steel. Wrought iron is iron with a low carbon content.Pig iron and cast iron have have a lower melting point than wrought iron or steel.

A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron, but also others such as lead or copper. With the first being that preheated blast air blown into the furnace reacts with the carbon in the form of coke to produce carbon monoxide and heat.
$2 C _{(s)} + {O _2} _{(g)} \rightarrow 2 CO _{(g)}$
All other reactions are associated with the middle region of blast furnace during smelting.The hot carbon monoxide is the reducing agent for the metal ore and reacts with the metal oxide to produce molten metal and carbon dioxide. 

The reaction of iron oxide with aluminium is used to join railway tracks. 

Iron from blast furnace is Pig Iron. It is intermediate to form Wrought Iron or Cast Iron. It is the first product from Blast Furnace. After applying some chemical reactions, pure iron will come.

In smelting process, ferric oxide gets reduced to Iron with the help of coke. The redox reaction is given by the option C.

Wrought iron or malleable iron is the purest form of commercial iron and is prepared from cast iron by oxidising impurities in a reverberatory furnace lined with haematite.

The reaction is called thermite reaction, in which $Al$ reduces the oxide of another metal as it forms stronger and more stable bonds with oxygen than the other metal.

Oxides of strong elecropositive metals such as K, Ca, Na, Al and Mg are very stable. It is difficult to reduce them into metallic state by carbon reduction.
Such metals are extracted by passing electricity through their fued chlorides/oxides/hydroxides.
So electrolytic extraction technique is used in extraction of highly electro positive metals.

Oxides of strong elecropositive metals such as $K, Ca, Na, Al$ and $Mg$ are very stable. It is difficult to reduce them into metallic state by carbon reduction.
Such metals are extracted by passing electricity through their fused chlorides/oxides/hydroxides.

Red bauxite is purified by Bayer's process, not Serpeck's method. Serpeck's method is typically used for the purification of white bauxite (containing silica as impurity).

Among all given option only $Na^+$ has less reduction potential than Zn so it can not be reduced by Zn.

The process of removal of unwanted materials from the ore is known as ore concentration. 

Heating farrow sulfate in a test tube following reaction takes place

Reaction of the process:

The puddling process is a historical method used to convert pig iron into wrought iron by removing impurities through oxidation in a reverberatory furnace.

Sintering is the process of forming a solid mass of material by heat and/or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or as a manufacturing process used with metals, ceramics, plastics, and other materials.

Smeltings main use is to produce a metal from its ore. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gasses or slag and leaving just the metal behind. The reducing agent is commonly a source of carbon.The carbon removes oxygen from the ore, leaving behind elemental metal. 

In extraction of tin from cassiterite-
$SnO _2+2C\rightarrow Sn+2CO$

In extraction of iron from haematite -
$Fe _2O _3+3CO\rightarrow 2Fe+3CO _2$

Iron pyrite $FeS _2$ is a sulphide ore for which froth floatation method is used.
Corundum is a crystalline form of aluminium oxide $Al _2O _3$ with traces of iron, titanium and chromium; for which electrolytic reduction method is used.

Highly electropositive metals cannot be extracted by carbon reduction process because of two reasons
(i) Metals combine with carbon to form carbides.
(ii) Loss of metal is more in vaporization.

The carbon reduction cannot be used for manganese and tungsten. This is because manganese and tungsten react with carbon to form manganese carbide and tungsten carbide respectively.

(A) Carbon reduces ferric oxide to iron. $Fe _2O _3+3C \rightarrow 2Fe + 3CO$.
Thus option A is correct.
(B) Carbon reduces zinc oxide to zinc. $ZnO+C \rightarrow {\triangle} {1673  K} Zn + CO \uparrow$.
Thus option B is correct.
(C) In presence of silica, carbon reduces calcium phosphate to free phosphorus.
$2 Ca _3(PO _4) _2 + 9 SiO _2 + 16 C  \rightarrow 6 CaSiO _3 + P _4 + 16 CO$
Thus option C is correct.
(D) Carbon reduces lead oxide to lead. $2PbO+C \rightarrow 2Pb+CO _2$.
Thus option D is correct.

Lead, iron and zinc can be extracted by smelting process . Aluminum can be extracted by electro metallurgy.

 The disadvantage of carbon reduction method are
(i) high temperature needed which is expensive and requires the use of a blast furnace
(ii) many metals combine with carbon forming carbides
(iii) carbon dioxide gas is released in the process which is green house gas.
(iii) metals produced contain significant amount of carbon. hence, metals obtained cannot be very pure.

The copper is extracted from sulphide ore by pyrometallurgy which involves reduction of the concentrated ore at high temperature.
This process is a dry process.
In this process, the sulphide ore is concentrated by froth floatation process.
In this process, the sulphide ore is not concentrated by leaching with dil sulphuric acid.
Thus, the statement B is incorrect and the statement A and C are correct.

Chemical equations for reduction of $Cu _2O$ using charcoal as a reducing agent : 

Hydrometallurgical extraction of copper involves leaching copper ores with sulfuric acid to produce copper sulfate solution, which is then processed to recover copper. All the listed reactions represent valid leaching processes for different copper ores.

All the four processes are correct.
$ZnO+C\overset{1100^{0}C}{\rightarrow}Zn+CO$
$Fe _{2}O _{3}+3C\rightarrow 2Fe+3CO$
$Ca _3(PO _4) _2,+,C,\rightarrow,2P +3CaO + CO _2$
$PbO,+,C,\rightarrow,Pb +CO$

Pyrometallurgy is the process of extraction and purification involving the application of heat.

By annealing, steel becomes soft.

Ferrochrome is produced by reduction of  $Cr-ore$ (an oxide of Chromium and iron) with coal and coke.

In the extraction of iron, the roasted ore is mixed with coke and lime stone (flux) and is then heated in the presence of air at high temperature in a furnace. Impurity of $SiO _2 $ is removed as calcium silicate $(CaSiO _3 slag)$.
$ CaCO _3\rightarrow CaO+CO _2$
$CaO+SiO _2\rightarrow CaSiO _3$

Flux is a substance which may be either acidic oxide $(Si{O} _{2})$ or basic oxide $(CaO, MgO)$. It combines with certain impurities (gangue particles) in order to form a substance called slag. This can be easily removed.

Pyrometallurgy employs high temperatures to carry out smelting and refining operations to extract metals from their minerals. 

Hydrometallurgy is a technique involving the use of aqueous chemistry for the recovery of metals from ores, concentrates, and recycled or residual materials. This process is used in extraction of less electro positive or less reactive metals like gold and silver by complex formation. 

Smelting is used to produce a base metal from its ore. The reducing agent is commonly a source of carbon such as coke, or in earlier times charcoal.

Hydrometallurgy involves formation of aqueous complex compounds and is used in extraction of less electro positive or less reactive metals like gold and silver. 

The process of extracting a metal from its oxide is known as 'smelting'. Most smelting processes involve direct reduction of the ore by carbon to metal and carbon dioxide. The production of primary aluminium is a good example of such a process.
Metals include copper, nickel, lead, zinc, silver, cobalt, gold, cadmium, etc.
Hence options A,B,C & D are correct.

Mercury containers are made of Iron because it does not form amalgum with iron.

During copper extraction, iron impurity (FeS) is removed by reacting it with silica (SiO2) to form iron silicate (FeSiO3), which is the slag.

Aluminium is more electropositive than Cr or Mn.
Hence, aluminum metal is frequently used as reducing agent for the extraction of metal such as chromium or manganese from their respective oxides.
The process of reduction is known as Aluminothermy. Thermite mixture $Fe _2O _3 + Al$ in 3:1 ratio is used.
$Cr _2 O _3 + 2Al       \rightarrow      Al _2O _3 + 2Cr$
$3 Mn _3 O _4 + 8 Al    \rightarrow     4 Al _2 O _3 + 9 Mn$

Hematite is the most important ore of iron.

$Fe _3O _4$ is the chemical formula of magnetite.

Wrought iron is purest form of iron.

The smelting of iron in a blast furnace involves all the following processes except Sublimation.

Haematite (Fe2O3) is an oxide ore. Magnetic separation is the most effective method for concentrating haematite because it is magnetic, allowing it to be separated from non-magnetic gangue particles.

It is the process by which a metal is obtained, either as the element or as a simple compound, from its ore by heating beyond the melting point, ordinarily in the presence of oxidizing agents, such as air, or reducing agents, such as coke. An oxidising agent is used in case of Al,Zn and Cu and so sodium reaction is not a smelting method.

Na can not be obtained by electrolysis of the aqueous solution of salt as hydrogen ions have higher reduction potential than $Na^+$ so hydrogen ions will reduce first and we will get hydrogen gas instead of Na metal by electrolysis of the aqueous solution,

The extraction of metal in the fused state is termed smelting. The ore is reduced by carbon to the free metal. A hot blast of air (sometimes with oxygen enrichment) is blown into the lower section of the furnace through a series of pipes . Formation of $CO$ from $CO _2$ and coke reduces the temperature of the middle region of blase furnace. Flux is a chemical substance which combines with gangue at higher temperaturesto form easily fusible material called slag which is not soluble in the molten metal. Limestone is taken blast furnace as basic flux. Silica present in the ore as gangue is converted to fusible slag by the process of oxidation  in flux.

The manufacture of iron from iron ore (like haematite) involves the reduction of iron oxide using a reducing agent such as carbon monoxide in a blast furnace.

Nitriding is the surface hardening process where nitrogen is added to the surface of steel parts using dissociated ammonia as the source. Gas nitriding develops a very hard case in a component at relatively low temperature. It is carried out at temperature below the transformation temperature of alloy steels and parts to be nitrided are heat treated to proper strength level and finally machined.

Thermite welding process exploits the difference in reactivity of different metals. Pure zinc rod is used as cathode while a block of impure zinc spelter is used as anode. Iron is generally refined by smelting process.Iron is alloyed with other metals and carbon prevents the oxidation of iron and formation of rust.

1: wrought iron carbon content 0.05-0.25%
2 : white and grey iron is the type of cast iron which contain 2.14-6.67% carbon. 
3: steel contain 0.008-2.14% carbon So D. Steel has least Carbon %

Iron reacts with oxygen and ions to make rust. after rust formation, it does not allow Iron to react with water.

Coke is a fuel with few impurities and a high carbon content, usually made from coal. Oven coke is used throughout the world in blast furnaces to make iron.

Purpose of smelting an ore is to reduce it. $Fe _{2}O _{3}$ is ore and $C$ is reductant.

In smelting, Iron ore is reduced to iron.

The percentage of Iron and Carbon determine whether it is cast Iron, Pig Iron, Steel or Alloys. Hence this is known as Ferrous Metallurgy. The main contribution is given by Iron as every type of Iron contains more than 90% of Iron.

Magnetic ceramics or ferrites are used to store computer data in the residual magnetic fields of hard ferrite cores.

Since, $CuCl _2$, $CuF _2$, $CuBr _2$ are stable and they exist but $CuI _2$ not, because Iodide ions are strong reducing agents, Therefore, copper (II) Iodide reduces to insoluble copper (I) iodide. Thus $CuI _2$ is not stable, so it does not exist in solution.

In the self reduction process, metal sulfide reacts with metal oxide to form free metal.
The conversion of metal ore to crude metal by self reduction process is carried for the pairs $Cu _2S, PbS$ and $PbS, HgS$.
For example cupric oxide reacts with cupric sulphide to form crude copper metal.
$2PbS+3O _2\rightarrow 2PbO+2SO _2$
$PbS+2PbO\rightarrow 3Pb+SO _2$ (self reduction)
$Cu _2S+2Cu _2O\rightarrow 6Cu+SO _2$
$HgS+2HgO\rightarrow 3Hg+SO _2$ 

The ore is reduced to metal by reduction with carbon. This is carried out during smelting. All the given four processes are correct.

Hydro metallurgy is a process of extraction of metals by converting their ores into aqueous solutions of metal compounds and reduction of these solutions using suitable reducing agents.Less electropositive metals like gold and silver are extracted by this method . 
Water, dilute acids or sodium cyanide solution are used to convert the metal present in the ore into solution.
Hence, the following steps are involved in hydrometallurgical process.
(B) $CuFeS _2 + 2H _2SO _4 \longrightarrow CuSO _4 + FeSO _4 + 2H _2S$
(C) $Ag _2S + 2NaCN \longrightarrow [Ag(CN) _2]^- + Na _2S$
(D) $CuCO _3 + H _2SO _4 \longrightarrow CuSO _4 + H _2O +CO _2$

Thermo-metallurgical process: